Is Pluto a planet after all?

HOW many planets are in the solar system? The official answer is eight - unless you happen to live in Illinois. Earlier this year, defiant Illinois state governors declared that Pluto had been unfairly demoted by the International Astronomical Union, the authority that sets the rules on all matters planetary.

Three years ago, the IAU decided to draw up the first scientific definition of the term planet. After days of stormy arguments at its general assembly in Prague, the delegates voted for a definition that excluded Pluto, downgrading it to the new category of dwarf planet.